The present invention relates in general to a method of and apparatus for providing a signal upon the arrival at a previously visited point in a well of equipment being run into or out of the well on a wire line. Such equipment may be used in drilling operations, production operations, remedial operations, or the like. Wire line operations in wells, particularly in the oil industry, are well known so that specific examples are unnecessary.
In running equipment in and out of a well on a wire line it is frequently desirable to be able to return to, or revisit, a given point in the well; the finite distance, or depth of the point, being immaterial to the repeated revisiting of the equipment to the point. The prevailing practice is to place a visible marker, commonly called a "flag" and hereinafter referred to as a "flag", on the wire line at an appropriate spot at the surface in the general area around the top of the well, hereinafter referred to as the "well head", when the wire line suspended equipment is at its operating position in the well. During subsequent trips into the well the flag provides a visual indication at the well head when the equipment has been returned to its operating position. Such a flag, when used on multi-strand wire lines is frequently a rag, leather straps, or pieces of rope tucked between strands of the wire line; or a piece of tape when used on single strand, or "piano wire", wire lines.
Similar procedures are followed in running equipment in and out of a well to avoid too high a running speed as the equipment reaches its destination so as to prevent possible damage to the equipment, the well installation and/or injury to personnel. The flag is visually detected at the well head by the operator in running the equipment in or out of the well and the running speed is reduced in anticipation of the arrival of the equipment at its destination.
As work progresses in a well, the attainment of greater depth in a drilling well, the lowering of the fluid level in a well being swabbed, or the reduction of fill in a well being bailed as examples; it is necessary to remove the previously placed flag and to establish a new point of reference on the wire line by placement of a new flag at a new point on the wire line. It is the preferred and accepted practice that the wire line not contain more than one flag at any one time so that there can be no question as to which flag is the "working marker", or "working flag". Often there will be as many as ten, or in a drilling well, several hundred changes of location necessary for the flag as the work progresses. In each instance it is required that the operation be shut down while the previous flag is removed, and again when the new flag is applied. In the case of multi-strand wire lines, mechanical separation of the wire line strands is required to either remove or insert the flag.
The foregoing practice has various disadvantages. For example, the application and removal of flags are time consuming and require physical exposure of personnel to the inherent dangers of wire line operations. The manually placed flags are subject to displacement along the cable and/or actual loss while running the equipment in or out of the well, or in using it to carry out its intended operation. The forcible spreading of the wire line strands of a multi-strand wire line in order to insert flags also results in abnormally stressing the wire line at the point of placing a flag. Further, visual detection of a flag requires a reduced speed in running in or out in anticipation of the arrival of the flag, which is time consuming. These and various other disadvantages of flags are avoided by the present invention, as will now be discussed.